The data_mutex is initialized too late, as it is needed for
each device driver's power control, causing an OOPS:

    dvb-usb: found a 'TerraTec/qanu USB2.0 Highspeed DVB-T Receiver' in warm state.
    BUG: unable to handle kernel NULL pointer dereference at           (null)
    IP: [<ffffffff846617af>] __mutex_lock_slowpath+0x6f/0x100 PGD 0
    Oops: 0002 [#1] SMP
    Modules linked in: dvb_usb_cinergyT2(+) dvb_usb
    CPU: 0 PID: 2029 Comm: modprobe Not tainted 4.9.0-rc4-dvbmod #24
    Hardware name: FUJITSU LIFEBOOK A544/FJNBB35 , BIOS Version 1.17 05/09/2014
    task: ffff88020e943840 task.stack: ffff8801f36ec000
    RIP: 0010:[<ffffffff846617af>]  [<ffffffff846617af>] __mutex_lock_slowpath+0x6f/0x100
    RSP: 0018:ffff8801f36efb10  EFLAGS: 00010282
    RAX: 0000000000000000 RBX: ffff88021509bdc8 RCX: 00000000c0000100
    RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffff88021509bdcc
    RBP: ffff8801f36efb58 R08: ffff88021f216320 R09: 0000000000100000
    R10: ffff88021f216320 R11: 00000023fee6c5a1 R12: ffff88020e943840
    R13: ffff88021509bdcc R14: 00000000ffffffff R15: ffff88021509bdd0
    FS:  00007f21adb86740(0000) GS:ffff88021f200000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 0000000000000000 CR3: 0000000215bce000 CR4: 00000000001406f0
    Call Trace:
       mutex_lock+0x16/0x25
       cinergyt2_power_ctrl+0x1f/0x60 [dvb_usb_cinergyT2]
       dvb_usb_device_init+0x21e/0x5d0 [dvb_usb]
       cinergyt2_usb_probe+0x21/0x50 [dvb_usb_cinergyT2]
       usb_probe_interface+0xf3/0x2a0
       driver_probe_device+0x208/0x2b0
       __driver_attach+0x87/0x90
       driver_probe_device+0x2b0/0x2b0
       bus_for_each_dev+0x52/0x80
       bus_add_driver+0x1a3/0x220
       driver_register+0x56/0xd0
       usb_register_driver+0x77/0x130
       do_one_initcall+0x46/0x180
       free_vmap_area_noflush+0x38/0x70
       kmem_cache_alloc+0x84/0xc0
       do_init_module+0x50/0x1be
       load_module+0x1d8b/0x2100
       find_symbol_in_section+0xa0/0xa0
       SyS_finit_module+0x89/0x90
       entry_SYSCALL_64_fastpath+0x13/0x94
    Code: e8 a7 1d 00 00 8b 03 83 f8 01 0f 84 97 00 00 00 48 8b 43 10 4c 8d 7b 08 48 89 63 10 4c 89 3c 24 41 be ff ff ff ff 48 89 44 24 08 <48> 89 20 4c 89 64 24 10 eb 1a 49 c7 44 24 08 02 00 00 00 c6 43 RIP  [<ffffffff846617af>] __mutex_lock_slowpath+0x6f/0x100 RSP <ffff8801f36efb10>
    CR2: 0000000000000000

So, move it to the struct dvb_usb_device and initialize it
before calling the driver's callbacks.
Reported-by: Jörg Otte <jrg.otte@gmail.com>
Tested-by: Jörg Otte <jrg.otte@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>